Thoughts on static electricity and ESD related issues from a leading consultant

Friday, May 20, 2005

>> I have one query, regarding the compliance of acceptable electro-static field>> strengths to 61340-5-1. I am unsure as what the standard states is an acceptable>> field potential for items such as vdu screens, printers, fans, walkmans>> etc. I have a figure of < 10Kv/m but am unsure where this came from.

< 10kV/m is the recommendation of 61340-5-2.

I interpret this as 10kV/m electrostatic field measured at the site of the ESDS parts. Another way of looking at it is that an object that has a surface voltage of 10kV must not come within 1 m of an ESDS, or 1 kV within 10 cm, or 100 V within 1 cm ......This rule of thumb applies to charged insulators.

Older CRT VDUs are certainly an issue, especially direct after switch-on or off. Newer VDUs - especially LCD types - may not be a problem. Laser printers are an issue - papers come out hot (and insulating) and highly charged. I prefer not to have them in the EPA especially as it usually means documentation is around and uncontrolled.

Other items such as radios, walkmans, computer keyboards etc - I don't believe they are generally an issue - but if in doubt measure the fields associated with them. If necessary keep them well away from ESDS. These items are often so contaminated with salts, grease and moisture from people's skin that you would be hard pushed to charge them up. Radios and walkmans can often be kept on a top shelf away from ESDS for example.

Charged conductors are a different matter - an isolated conductor of any significant size charged to 100V within 1 cm of an ESDS could be a risk because of machine model ESD if it touched the part. Conductors should be grounded (and therefore have no significant voltage).

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About Me

Dr Jeremy Smallwood has been working as a static electricity consultant since 1987. He started his company Electrostatic Solutions Ltd to give top level static electricity research and development and consultancy services in 1997.